Sailfin Molly

The natural lifespan of sailfin mollies is short, particularly in the case of the males, which may live less than a year after achieving sexual maturity. Depending upon environmental conditions, sailfin mollies may become reproductive in less than a year. Sailfin mollies are small fish. At one year of age, males typically range in size from 0.5 to 3 in (13 to 76 mm) SL, while mature females are likely to be 0.5 to 2.5 in (13 to 64 mm) inch SL. The size of adult males is directly correlated with population density. The greater the population, the smaller the average size of males. The maximum recorded size for this species is 150 mm (5.9 in) TL.

The sailfin molly is found in freshwater and brackish habitats from North Carolina to Texas and the Yucatán Peninsula of Mexico. Preferring coastal marshes fed by lowland streams, as well as mangrove swamps, deltas and estuaries, the sailfin molly is very common in peninsular Florida and around the entire Gulf of Mexico. Invasive and introduced populations have been established in New Zealand, in the western U.S., and Hawaii. Sailfin mollies introduced to California have caused a decline in populations of the federally protected and endangered desert pupfish (Cyprinodon macularius). It is also invasive to Iraq, where it thrives in the Persian Gulf waters at the confluence of the Tigris and Euphrates river deltas, threatening to outcompete many killifish species endemic to the region.

Sailfin mollies feed primarily upon algae and other plant materials, although they will consume a number of aquatic invertebrates, including the larvae of mosquitoes.

Sailfin mollies are members of the lower end of the food chain. As such, they are prey for various animals, including aquatic insects, other fishes, reptiles, amphibians, birds and mammals. Specific examples include: giant water bugs (Belostomatidae), largemouth bass (Micropterus salmoides), American alligator (Alligator mississippiensis), bullfrog (Rana catesbeiana), snowy egret (Egretta thula), and raccoon (Procyon lotor).

Fertilization is internal, and is accomplished by means of highly modified fin elements within the anal fin of males that form a structure known as the gonopodium. Sailfin mollies produce broods of 10–140 live young, depending on maturity and size, and females may store sperm long after the demise of their relatively short-lived mates. The gestation period for this species is about three to four weeks, depending upon temperature, and a single female may give birth on multiple occasions throughout the year. Although sex ratios of the broods are balanced, adult populations tend to be largely female, as males appear to suffer higher rates of mortality due to a greater susceptibility to predators and disease as a consequence of their brighter colors and a life devoted to frenzied breeding. No parental care is exhibited by this species.

The sailfin molly is of considerable interest and value to aquarists, and many artificially selected varieties are produced and sold in pet shops. Wild sailfin mollies are also bred as feeder fish for larger carnivorous fish, though usually guppies are used for that. Naturally occurring populations control mosquito populations by feeding on the larvae and pupae of these pests.